CCAAT/enhancer binding protein gene promoter: binding of nuclear factors during differentiation of 3T3-L1 preadipocytes

AP-1/C-FOS and AP-1/FRA2 differentially regulate early and late adipogenic differentiation of mesenchymal stem cells

Obesity is defined as an abnormal accumulation of adipose tissue in the body and is a major global health problem due to increased morbidity and mortality. Adipose tissue is made up of adipocytes, which are fat-storing cells, and the differentiation of these fat cells is known as adipogenesis. Several transcription factors (TFs) such as CEBPβ, CEBPα, PPARγ, GATA, and KLF have been reported to play a key role in adipogenesis. In this study, we report one more TF AP-1, which is found to be involved in adipogenesis. Human mesenchymal stem cells  were differentiated into adipocytes, and the expression pattern of different subunits of AP-1 was examined during adipogenesis. It was observed that C-FOS was predominantly expressed at an early stage (Day 2), whereas FRA2 expression peaked at later stages (Days 6 and 8) of adipogenesis. Chromatin immunoprecipitation-sequencing analysis revealed that C-FOS binds mainly to the promoters of WNT1, miR-30a, and ANAPC7 and regulates their expression during mitotic clonal expansion. In contrast, FRA2 binds to the promoters of CIDEA, NOTCH1, ARAF, and MYLK, regulating their expression and lipid metabolism. Data obtained clearly indicate that the differential expression of C-FOS and FRA2 is crucial for different stages of adipogenesis. This also raises the possibility of considering AP-1 as a therapeutic target for treating obesity and related disorders.

CCAAT/enhancer-binding protein α-dependent regulation of granule formation in mast cells by intestinal bacteria

The antiallergic effects of gut microbiota have been attracting attention in recent years, but the underlying cellular and molecular mechanisms have not yet been fully understood. In this study, we aimed to investigate these mechanisms specifically focusing on mast cells. Mast cells retain intracellular granules containing various inflammatory mediators such as histamine, which are released outside the cells upon IgE and allergen stimulation. We previously reported that increased expression of the transcription factor, CCAAT/enhancer-binding protein α (C/EBPα), suppresses granule formation in mast cells and that Lacticaseibacillus casei JCM1134T (LC) upregulates C/EBPα levels. Here, granule formation in mouse bone marrow-derived mast cells was suppressed in a MyD88-dependent manner after LC treatment due to C/EBPα-dependent downregulation of the genes encoding serglycin (SRGN) and mast cell protease 4 (Mcpt4). Furthermore, C/EBPα expression was regulated by DNA methylation in the 5' region far upstream of the transcription start site. LC suppressed DNA methylation of specific CpG motifs in the 5' region of the C/EBPα gene. These results conclude that specific gut microbial components, such as those from LC, suppress granule formation in mast cells by inhibiting SRGN and Mcpt4 expression via reduced C/EBPα gene methylation.

Gene expression and characterization of clonally derived murine embryonic brown and brite adipocytes

White adipocytes store energy, while brown and brite adipocytes release heat via nonshivering thermogenesis. In this study, we characterized two murine embryonic clonal preadipocyte lines, EB5 and EB7, each displaying unique gene marker expression profiles. EB5 cells differentiate into brown adipocytes, whereas EB7 cells into brite (also known as beige) adipocytes. To draw a comprehensive comparison, we contrasted the gene expression patterns, adipogenic capacity, as well as carbohydrate and lipid metabolism of these cells to that of F442A, a well-known white preadipocyte and adipocyte model. We found that commitment to differentiation in both EB5 and EB7 cells can be induced by 3-Isobutyl-1-methylxanthine/dexamethasone (Mix/Dex) and staurosporine/dexamethasone (St/Dex) treatments. Additionally, the administration of rosiglitazone significantly enhances the brown and brite adipocyte phenotypes. Our data also reveal the involvement of a series of genes in the transcriptional cascade guiding adipogenesis, pinpointing GSK3β as a critical regulator for both EB5 and EB7 adipogenesis. In a developmental context, we observe that, akin to brown fat progenitors, brite fat progenitors make their appearance in murine development by 11-12 days of gestation or potentially earlier. This result contributes to our understanding of adipocyte lineage specification during embryonic development. In conclusion, EB5 and EB7 cell lines are valuable for research into adipocyte biology, providing insights into the differentiation and development of brown and beige adipocytes. Furthermore, they could be useful for the characterization of drugs targeting energy balance for the treatment of obesity and metabolic diseases.

Impaired Remodeling of White Adipose Tissue in Obesity and Aging: From Defective Adipogenesis to Adipose Organ Dysfunction

The adipose organ adapts and responds to internal and environmental stimuli by remodeling both its cellular and extracellular components. Under conditions of energy surplus, the subcutaneous white adipose tissue (WAT) is capable of expanding through the enlargement of existing adipocytes (hypertrophy), followed by de novo adipogenesis (hyperplasia), which is impaired in hypertrophic obesity. However, an impaired hyperplastic response may result from various defects in adipogenesis, leading to different WAT features and metabolic consequences, as discussed here by reviewing the results of the studies in animal models with either overexpression or knockdown of the main molecular regulators of the two steps of the adipogenesis process. Moreover, impaired WAT remodeling with aging has been associated with various age-related conditions and reduced lifespan expectancy. Here, we delve into the latest advancements in comprehending the molecular and cellular processes underlying age-related changes in WAT function, their involvement in common aging pathologies, and their potential as therapeutic targets to influence both the health of elderly people and longevity. Overall, this review aims to encourage research on the mechanisms of WAT maladaptation common to conditions of both excessive and insufficient fat tissue. The goal is to devise adipocyte-targeted therapies that are effective against both obesity- and age-related disorders.

Autophagy in adipogenesis: Molecular mechanisms and regulation by bioactive compounds

White adipose tissue expands rapidly due to increased adipocyte number (hyperplasia) and size (hypertrophy), which results in obesity. Adipogenesis is a process of the formation of mature adipocytes from precursor cells. Additionally, obesity-related metabolic complications, such as fatty liver and insulin resistance, are linked to adipogenesis. On the contrary, autophagy is a catabolic process; essential to maintain cellular homeostasis via the degradation or recycling of unnecessary or damaged components. Importantly, autophagy dictates obesity and adipogenesis. Hence, a clear understanding of how autophagy regulates adipogenesis is crucial for drug development and the prevention and treatment of obesity and its associated disorders, such as type 2 diabetes, cardiovascular disease, and cancer. In this review, we highlighted recent findings regarding the crosstalk between adipogenesis and autophagy, as well as the molecules involved. Furthermore, the review discussed how bioactive compounds regulate adipogenesis by manipulating autophagy and underlying molecular mechanisms. Based on in vitro and animal studies, we summarized the effects of bioactive compounds on adipogenesis and autophagy. Hence, human studies are necessary to validate the effectiveness and optimal dosage of these bioactive compounds.

Adipocyte Biology from the Perspective of In Vivo Research: Review of Key Transcription Factors

Obesity and type 2 diabetes are both significant contributors to the contemporary pandemic of non-communicable diseases. Both disorders are interconnected and associated with the disruption of normal homeostasis in adipose tissue. Consequently, exploring adipose tissue differentiation and homeostasis is important for the treatment and prevention of metabolic disorders. The aim of this work is to review the consecutive steps in the postnatal development of adipocytes, with a special emphasis on in vivo studies. We gave particular attention to well-known transcription factors that had been thoroughly described in vitro, and showed that the in vivo research of adipogenic differentiation can lead to surprising findings.

The complex landscape of haematopoietic lineage commitments is encoded in the coarse-grained endogenous network

Haematopoietic lineage commitments are presented by a canonical roadmap in which haematopoietic stem cells or multipotent progenitors (MPPs) bifurcate into progenitors of more restricted lineages and ultimately mature to terminally differentiated cells. Although transcription factors playing significant roles in cell-fate commitments have been extensively studied, integrating such knowledge into the dynamic models to understand the underlying biological mechanism remains challenging. The hypothesis and modelling approach of the endogenous network has been developed previously and tested in various biological processes and is used in the present study of haematopoietic lineage commitments. The endogenous network is constructed based on the key transcription factors and their interactions that determine haematopoietic cell-fate decisions at each lineage branchpoint. We demonstrate that the process of haematopoietic lineage commitments can be reproduced from the landscape which orchestrates robust states of network dynamics and their transitions. Furthermore, some non-trivial characteristics are unveiled in the dynamical model. Our model also predicted previously under-represented regulatory interactions and heterogeneous MPP states by which distinct differentiation routes are intermediated. Moreover, network perturbations resulting in state transitions indicate the effects of ectopic gene expression on cellular reprogrammes. This study provides a predictive model to integrate experimental data and uncover the possible regulatory mechanism of haematopoietic lineage commitments.

The AML-associated K313 mutation enhances C/EBPα activity by leading to C/EBPα overexpression

Mutations in the transcription factor C/EBPα are found in ~10% of all acute myeloid leukaemia (AML) cases but the contribution of these mutations to leukemogenesis is incompletely understood. We here use a mouse model of granulocyte progenitors expressing conditionally active HoxB8 to assess the cell biological and molecular activity of C/EBPα-mutations associated with human AML. Both N-terminal truncation and C-terminal AML-associated mutations of C/EBPα substantially altered differentiation of progenitors into mature neutrophils in cell culture. Closer analysis of the C/EBPα-K313-duplication showed expansion and prolonged survival of mutant C/EBPα-expressing granulocytes following adoptive transfer into mice. C/EBPα-protein containing the K313-mutation further showed strongly enhanced transcriptional activity compared with the wild-type protein at certain promoters. Analysis of differentially regulated genes in cells overexpressing C/EBPα-K313 indicates a strong correlation with genes regulated by C/EBPα. Analysis of transcription factor enrichment in the differentially regulated genes indicated a strong reliance of SPI1/PU.1, suggesting that despite reduced DNA binding, C/EBPα-K313 is active in regulating target gene expression and acts largely through a network of other transcription factors. Strikingly, the K313 mutation caused strongly elevated expression of C/EBPα-protein, which could also be seen in primary K313 mutated AML blasts, explaining the enhanced C/EBPα activity in K313-expressing cells.

Hematopoietically-expressed homeobox protein HHEX regulates adipogenesis in preadipocytes

Obesity is a key health problem and is associated with a high risk of type 2 diabetes and other metabolic diseases. Increased weight as well as dysregulation of adipocyte homeostasis are the main drivers of obesity. Pathological adipogenesis plays a central role in obesity-related complications such as type 2 diabetes, hypertension and others. Thus, an understanding of the molecular mechanisms involved in physiological and pathogenic adipogenesis can help to develop new strategies to prevent or cure obesity and related diseases. Previously, genetic polymorphisms in the HHEX gene that encodes the homeobox transcription factor HEX (PRH) were found to be associated with type 2 diabetes and high body mass index at birth by GWAS in distinct human populations. To understand whether HHEX has a regulatory function in adipogenesis, we performed RNAi-mediated knockdown of Hhex in preadipocyte cell line 3T3-L1 in vitro, and studied changes in the efficacy of adipogenesis. We found that Hhex knockdown blocks adipogenesis in preadipocytes in a dose-dependent manner and leads to a significant decrease of PPAR-gamma protein - the main regulator of adipogenesis. We also propose that Hhex can play an important role in adipocyte differentiation by affecting the level of the PPAR-gamma protein. Our study supports the claim that Hhex plays an important role in adipocyte differentiation program and can contribute to fat tissue homeostasis.

ACOX1, regulated by C/EBPα and miR-25-3p, promotes bovine preadipocyte adipogenesis

Acyl-coenzyme A oxidase 1 (ACOX1) is the first and rate-limiting enzyme in peroxisomal fatty acid β-oxidation of fatty acids. Previous studies have reported that ACOX1 was correlated with the meat quality of livestock, while the role of ACOX1 in intramuscular adipogenesis of beef cattle and its transcriptional and post-transcriptional regulatory mechanisms remain unclear. In the present study, gain-of-function and loss-of-function assays demonstrated that ACOX1 positively regulated the adipogenesis of bovine intramuscular preadipocytes. The C/EBPα-binding sites in the bovine ACOX1 promoter region at -1142 to -1129 bp, -831 to -826 bp, and -303 to -298 bp were identified by promoter deletion analysis and site-directed mutagenesis. Electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP) further showed that these three regions are C/EBPα-binding sites, both in vitro and in vivo, indicating that C/EBPα directly interacts with the bovine ACOX1 promoter and inhibits its transcription. Furthermore, the results from bioinformatics analysis, dual luciferase assay, site-directed mutagenesis, qRT-PCR, and Western blotting demonstrated that miR-25-3p directly targeted the ACOX1 3'UTR (3'UTR). Taken together, our findings suggest that ACOX1, regulated by transcription factor C/EBPα and miR-25-3p, promotes adipogenesis of bovine intramuscular preadipocytes via regulating peroxisomal fatty acid β-oxidation.

Molecular Mechanism of Stem Cell Differentiation into Adipocytes and Adipocyte Differentiation of Malignant Tumor

Adipogenesis is the process through which preadipocytes differentiate into adipocytes. During this process, the preadipocytes cease to proliferate, begin to accumulate lipid droplets, and develop morphologic and biochemical characteristics of mature adipocytes. Mesenchymal stem cells (MSCs) are a type of adult stem cells known for their high plasticity and capacity to generate mesodermal and nonmesodermal tissues. Many mature cell types can be generated from MSCs, including adipocyte, osteocyte, and chondrocyte. The differentiation of stem cells into multiple mature phenotypes is at the basis for tissue regeneration and repair. Cancer stem cells (CSCs) play a very important role in tumor development and have the potential to differentiate into multiple cell lineages. Accumulating evidence has shown that cancer cells can be induced to differentiate into various benign cells, such as adipocytes, fibrocytes, osteoblast, by a variety of small molecular compounds, which may provide new strategies for cancer treatment. Recent studies have reported that tumor cells undergoing epithelial-to-mesenchymal transition can be induced to differentiate into adipocytes. In this review, molecular mechanisms, signal pathways, and the roles of various biological processes in adipose differentiation are summarized. Understanding the molecular mechanism of adipogenesis and adipose differentiation of cancer cells may contribute to cancer treatments that involve inducing differentiation into benign cells.

Analysis of the Bovine DLK1 Gene Polymorphism and Its Relation to Lipid Metabolism in Chinese Simmental

In this study, we precisely constructed and transfected the overexpression and interference vectors in BFFs to evaluate the role of DLK1 gene on lipid metabolism in vitro. The expression of of DLK1 in the mRNA and protein level tended to reduce, and TGs were significantly increased in the pGPU6-shDLK1 group compared to the control group (p < 0.05). The expression of DLK1 in the mRNA and protein level were increased in the pBI-CMV3-DLK1 group compared to the control group, and the TGs content showed a significant decrease in the pBI-CMV3-DLK1 group (p < 0.05). Meanwhile, we used the restriction fragment length polymorphism (RFLP-PCR) detection method to screen SNPs further to explore and analyze the relationship between the gene and the economic traits of 28-month-old Chinese Simmental and the fatty acids composition of cattle longissimus muscle. The result showed that two SNPs, IVS3 + 478 C>T and IVS3 + 609 T>G, were identified as being significantly associated with carcass and meat quality traits in Chinese Simmental, such as the carcass fat coverage rate, loin eye muscle area, and fat color score. In summary, our results indicated that DLK1 can affect lipid metabolism in bovine and these two SNPs might be applied as genetic markers of meat quality traits for beef cattle breeding.

The Role of Autophagy in White Adipose Tissue Function: Implications for Metabolic Health

White adipose tissue (WAT) is a highly adaptive endocrine organ that continuously remodels in response to nutritional cues. WAT expands to store excess energy by increasing adipocyte number and/or size. Failure in WAT expansion has serious consequences on metabolic health resulting in altered lipid, glucose, and inflammatory profiles. Besides an impaired adipogenesis, fibrosis and low-grade inflammation also characterize dysfunctional WAT. Nevertheless, the precise mechanisms leading to impaired WAT expansibility are yet unresolved. Autophagy is a conserved and essential process for cellular homeostasis, which constitutively allows the recycling of damaged or long-lived proteins and organelles, but is also highly induced under stress conditions to provide nutrients and remove pathogens. By modulating protein and organelle content, autophagy is also essential for cell remodeling, maintenance, and survival. In this line, autophagy has been involved in many processes affected during WAT maladaptation, including adipogenesis, adipocyte, and macrophage function, inflammatory response, and fibrosis. WAT autophagy dysregulation is related to obesity and diabetes. However, it remains unclear whether WAT autophagy alteration in obese and diabetic patients are the cause or the consequence of WAT malfunction. In this review, current data regarding these issues are discussed, focusing on evidence from human studies.

Ellagic Acid and Urolithins A and B Differentially Regulate Fat Accumulation and Inflammation in 3T3-L1 Adipocytes While Not Affecting Adipogenesis and Insulin Sensitivity

Ellagic acid (EA) is a component of ellagitannins, present in crops such as pecans, walnuts, and many berries, which metabolized by the gut microbiota forms urolithins A, B, C, or D. In this study, ellagic acid, as well as urolithins A and B, were tested on 3T3-L1 preadipocytes for differentiation and lipid accumulation. In addition, inflammation was studied in mature adipocytes challenged with lipopolysaccharide (LPS). Results indicated that EA and urolithins A and B did not affect differentiation (adipogenesis) and only EA and urolithin A attenuated lipid accumulation (lipogenesis), which seemed to be through gene regulation of glucose transporter type 4 (GLUT4) and adiponectin. On the other hand, gene expression of cytokines and proteins associated with the inflammation process indicate that urolithins and EA differentially inhibit tumor necrosis factor alpha (TNFα), inducible nitric oxide synthase (iNOS), interleukin 6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1). Urolithins A and B were found to reduce nuclear levels of phosphorylated nuclear factor κB (p-NF-κB), whereas all treatments showed expression of nuclear phosphorylated protein kinase B (p-AKT) in challenged LPS cells when treated with insulin, indicating the fact that adipocytes remained insulin sensitive. In general, urolithin A is a compound able to reduce lipid accumulation, without affecting the protein expression of peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer binding protein-α (c/EBPα), and PPARα, whereas EA and urolithin B were found to enhance PPARγ and c/EBPα protein expressions as well as fatty acid (FA) oxidation, and differentially affected lipid accumulation.

Induction of DEAD Box helicase 5 in early adipogenesis is regulated by Ten-eleven translocation 2

Dead box helicase 5 (DDX5) is an RNA helicase that is has cellular function on RNA splicing and transcriptional regulation. It has been reported to be involved in cell differentiation including adipogenesis. However, it is not clear how DDX5 is regulated during adipogenesis. Our previous report demonstrated that the Ten-eleven translocation methyl-cytosine dioxygenase 2 (TET2) is required for adipogenesis. This study was aimed to investigate DDX5 as a direct target of TET2 upon adipogenic induction of 3T3-L1 preadipocyte. Microarray-based screening of differentially expressed genes upon TET2 knockdown identified genes involved in cell cycle, DNA replication, and ribosome biology as major targets of TET2 in the initial step of adipogenic induction. The Ddx5 gene was identified and validated as the target. TET2-mediated epigenetic regulation of the Ddx5 gene was measured by two independent methods including immunoprecipitation against 5-hydroxymethylcytosine (5hmC) and 5-methylcytosine (5mC) as well as EpiMark 5hmC and 5mC analysis. Ddx5 expression was downregulated upon TET2 knockdown, coincided with a significant decrease of 5hmC at the Ddx5 locus. DDX5 knockdown significantly suppressed adipogenesis, while DDX5 overexpression promoted it. Importantly, DDX5 overexpression, when co-transfected, rescued the process of adipogenesis, which was hindered by TET2 siRNA treatment. The findings suggest TET2-mediated regulation of the Ddx5 gene is required for an initial step of adipogenesis.

Sulforaphene Suppresses Adipocyte Differentiation via Induction of Post-Translational Degradation of CCAAT/Enhancer Binding Protein Beta (C/EBPβ)

Adipocyte differentiation (adipogenesis) is a crucial process that determines the total number and size of mature adipocytes that will develop. In this study, the anti-adipogenic effect of sulforaphene (SFEN), a dietary isothiocyanate (ITC) derived from radish, is investigated both in 3T3-L1 pre-adipocytes and in human adipose tissue-derived stem cells. The results revealed that SFEN significantly inhibit adipogenic cocktail-induced adipocyte differentiation and lipid accumulation at the early stage of adipogenesis. Additionally, the effects are more potent compared to those of other ITCs derived from various cruciferous vegetables. As a related molecular mechanism of action, SFEN promotes the post-translational degradation of CCAAT/enhancer-binding protein (C/EBP) β by decreasing the stability of C/EBPβ, which is responsible for decreasing the expression of master regulatory proteins such as peroxisome proliferator-activated receptor γ and C/EBPα. Collectively, these results suggest that the intake of SFEN-enriched natural materials could be helpful as a strategy for preventing obesity.

Ergosterol Peroxide from the Medicinal Mushroom Ganoderma lucidum Inhibits Differentiation and Lipid Accumulation of 3T3-L1 Adipocytes

Ergosterol peroxide is a natural compound of the steroid family found in many fungi, and it possesses antioxidant, anti-inflammatory, anticancer and antiviral activities. The anti-obesity activity of several edible and medicinal mushrooms has been reported, but the effect of mushroom-derived ergosterol peroxide on obesity has not been studied. Therefore, we analyzed the effect of ergosterol peroxide on the inhibition of triglyceride synthesis at protein and mRNA levels and differentiation of 3T3-L1 adipocytes. Ergosterol peroxide inhibited lipid droplet synthesis of differentiated 3T3-L1 cells, expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAT/enhancer-binding protein alpha (C/EBPα), the major transcription factors of differentiation, and also the expression of sterol regulatory element-binding protein-1c (SREBP-1c), which promotes the activity of PPARγ, resulting in inhibition of differentiation. It further inhibited the expression of fatty acid synthase (FAS), fatty acid translocase (FAT), and acetyl-coenzyme A carboxylase (ACC), which are lipogenic factors. In addition, it inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs) involved in cell proliferation and activation of early differentiation transcription factors in the mitotic clonal expansion (MCE) stage. As a result, ergosterol peroxide significantly inhibited the synthesis of triglycerides and differentiation of 3T3-L1 cells, and is, therefore, a possibile prophylactic and therapeutic agent for obesity and related metabolic diseases.

Shockwaves Suppress Adipocyte Differentiation via Decrease in PPARγ

Adipogenesis is a crucial cellular process that contributes to the expansion of adipose tissue in obesity. Shockwaves are mechanical stimuli that transmit signals to cause biological responses. The purpose of this study is to evaluate the effects of shockwaves on adipogenesis. We treated 3T3L-1 cells and human primary preadipocytes for differentiation with or without shockwaves. Western blots and quantitative real-time reverse transcriptase PCR (qRT-PCR) for adipocyte markers including peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT-enhancer-binding proteins (C/EBPα) were performed. Extracellular adenosine triphosphate (ATP) and intracellular cyclic adenosine monophosphate (cAMP) levels, which are known to affect adipocyte differentiation, were measured. Shockwave treatment decreased intracellular lipid droplet accumulation in primary human preadipocytes and 3T3-L1 cells after 11–12 days of differentiation. Levels of key adipogenic transcriptional factors PPARγ and/or C/EBPα were lower in shockwave-treated human primary preadipocytes and 3T3L-1 cells after 12–13 days of differentiation than in shockwave-untreated cells. Shockwave treatment induced release of extracellular ATP from preadipocytes and decreased intracellular cAMP levels. Shockwave-treated preadipocytes showed a higher level of β-catenin and less PPARγ expression than shockwave-untreated cells. Supplementation with 8-bromo-cAMP analog after shockwave treatment rescued adipocyte differentiation by preventing the effect of shockwaves on β-catenin, Wnt10b mRNA, and PPARγ expression. Low-energy shockwaves suppressed adipocyte differentiation by decreasing PPARγ. Our study suggests an insight into potential uses of shockwave-treatment for obesity.

HoxA9 binds and represses the Cebpa +8 kb enhancer

C/EBPα plays a key role in specifying myeloid lineage development. HoxA9 is expressed in myeloid progenitors, with its level diminishing during myeloid maturation, and HOXA9 is over-expressed in a majority of acute myeloid leukemia cases, including those expressing NUP98-HOXD13. The objective of this study was to determine whether HoxA9 directly represses Cebpa gene expression. We find 4-fold increased HoxA9 and 5-fold reduced Cebpa in marrow common myeloid and LSK progenitors from Vav-NUP98-HOXD13 transgenic mice. Conversely, HoxA9 decreases 5-fold while Cebpa increases during granulocytic differentiation of 32Dcl3 myeloid cells. Activation of exogenous HoxA9-ER in 32Dcl3 cells reduces Cebpa mRNA even in the presence of cycloheximide, suggesting direct repression. Cebpa transcription in murine myeloid cells is regulated by a hematopoietic-specific +37 kb enhancer and by a more widely active +8 kb enhancer. ChIP-Seq analysis of primary myeloid progenitor cells expressing exogenous HoxA9 or HoxA9-ER demonstrates that HoxA9 localizes to both the +8 kb and +37 kb Cebpa enhancers. Gel shift analysis demonstrates HoxA9 binding to three consensus sites in the +8 kb enhancer, but no affinity for the single near-consensus site present in the +37 kb enhancer. Activity of a Cebpa +8 kb enhancer/promoter-luciferase reporter in 32Dcl3 or MOLM14 myeloid cells is increased ~2-fold by mutation of its three HOXA9-binding sites, suggesting that endogenous HoxA9 represses +8 kb Cebpa enhancer activity. In contrast, mutation of five C/EBPα-binding sites in the +8 kb enhancer reduces activity 3-fold. Finally, expression of a +37 kb enhancer/promoter-hCD4 transgene reporter is reduced ~2-fold in marrow common myeloid progenitors when the Vav-NUP98-HOXD13 transgene is introduced. Overall, these data support the conclusion that HoxA9 represses Cebpa expression, at least in part via inhibition of its +8 kb enhancer, potentially allowing normal myeloid progenitors to maintain immaturity and contributing to the pathogenesis of acute myeloid leukemia associated with increased HOXA9.

Natural Products and Obesity: A Focus on the Regulation of Mitotic Clonal Expansion during Adipogenesis

Obesity is recognized as a worldwide health crisis. Obesity and its associated health complications such as diabetes, dyslipidemia, hypertension, and cardiovascular diseases impose a big social and economic burden. In an effort to identify safe, efficient, and long-term effective methods to treat obesity, various natural products with potential for inhibiting adipogenesis were revealed. This review aimed to discuss the molecular mechanisms underlying adipogenesis and the inhibitory effects of various phytochemicals, including those from natural sources, on the early stage of adipogenesis. We discuss key steps (proliferation and cell cycle) and their regulators (cell-cycle regulator, transcription factors, and intracellular signaling pathways) at the early stage of adipocyte differentiation as the mechanisms responsible for obesity.

Impaired Adipogenesis and Dysfunctional Adipose Tissue in Human Hypertrophic Obesity

The subcutaneous adipose tissue (SAT) is the largest and best storage site for excess lipids. However, it has a limited ability to expand by recruiting and/or differentiating available precursor cells. When inadequate, this leads to a hypertrophic expansion of the cells with increased inflammation, insulin resistance, and a dysfunctional prolipolytic tissue. Epi-/genetic factors regulate SAT adipogenesis and genetic predisposition for type 2 diabetes is associated with markers of an impaired SAT adipogenesis and development of hypertrophic obesity also in nonobese individuals. We here review mechanisms for the adipose precursor cells to enter adipogenesis, emphasizing the role of bone morphogenetic protein-4 (BMP-4) and its endogenous antagonist gremlin-1, which is increased in hypertrophic SAT in humans. Gremlin-1 is a secreted and a likely important mechanism for the impaired SAT adipogenesis in hypertrophic obesity. Transiently increasing BMP-4 enhances adipogenic commitment of the precursor cells while maintained BMP-4 signaling during differentiation induces a beige/brown oxidative phenotype in both human and murine adipose cells. Adipose tissue growth and development also requires increased angiogenesis, and BMP-4, as a proangiogenic molecule, may also be an important feedback regulator of this. Hypertrophic obesity is also associated with increased lipolysis. Reduced lipid storage and increased release of FFA by hypertrophic SAT are important mechanisms for the accumulation of ectopic fat in the liver and other places promoting insulin resistance. Taken together, the limited expansion and storage capacity of SAT is a major driver of the obesity-associated metabolic complications.

Chlorogenic Acid Functions as a Novel Agonist of PPARγ2 during the Differentiation of Mouse 3T3-L1 Preadipocytes

Rosiglitazone (RG) is a well-known activator of peroxisome proliferator-activated receptor-gamma (PPARγ) and used to treat hyperglycemia and type 2 diabetes; however, its clinical application has been confounded by adverse side effects. Here, we assessed the roles of chlorogenic acid (CGA), a phenolic secondary metabolite found in many fruits and vegetables, on the differentiation and lipolysis of mouse 3T3-L1 preadipocytes. The results showed that CGA promoted differentiation in vitro according to oil red O staining and quantitative polymerase chain reaction assays. As a potential molecular mechanism, CGA downregulated mRNA levels of the adipocyte differentiation-inhibitor gene Pref1 and upregulated those of major adipogenic transcriptional factors (Cebpb and Srebp1). Additionally, CGA upregulated the expression of the differentiation-related transcriptional factor PPARγ2 at both the mRNA and protein levels. However, following CGA intervention, the accumulation of intracellular triacylglycerides following preadipocyte differentiation was significantly lower than that in the RG group. Consistent with this, our data indicated that CGA treatment significantly upregulated the expression of lipogenic pathway-related genes Plin and Srebp1 during the differentiation stage, although the influence of CGA was weaker than that of RG. Notably, CGA upregulated the expression of the lipolysis-related gene Hsl, whereas it did not increase the expression of the lipid synthesis-related gene Dgat1. These results demonstrated that CGA might function as a potential PPARγ agonist similar to RG; however, the impact of CGA on lipolysis in 3T3-L1 preadipocytes differed from that of RG.

R-Limonene Enhances Differentiation and 2-Deoxy-D-Glucose Uptake in 3T3-L1 Preadipocytes by Activating the Akt Signaling Pathway

Adipocyte is an important place for lipid storage. Defects in lipid storage in adipocytes can lead to lipodystrophy and lipid accumulation in muscle, liver, and other organs. It is the condition of mixed dyslipidemia which may favor the development of insulin resistance via lipotoxic mechanisms. Our objective of the study was to investigate the potential role of R-limonene (LM) on differentiation, lipid storage, and 2-deoxy-D-glucose (2DG) uptake in 3T3-L1 preadipocytes. Genes and proteins associated with differentiation, lipid accumulation, 2DG uptake and its signaling pathways in the adipocytes were analyzed using qPCR and western blot methods. LM treatment increased differentiation, lipid accumulation, and the expression of adipogenic and lipogenic markers such as C/EBP-α, C/EBP-β, PPARγ, SREBP-1, RXR, FAS, and adiponectin. However, the LM concentration at 10μM decreased (p < 0.05) adipogenesis and lipogenesis via regulating key transcriptional factors. LM treatment increased activation of Akt by increasing its phosphorylation, but p44/42 activation was not altered. MK-2206, an Akt specific inhibitor, reduced the activation of Akt phosphorylation whereas LM treatment aborted the MK-2206 mediated inhibition of Akt activation. LM enhanced glucose uptake in differentiated adipocytes. Overall data suggested that LM treatment favored lipid storage and glucose uptake in adipocytes via activation of key transcriptional factors through activation of Akt phosphorylation in 3T3-L1 adipocytes.

Combination of Garcinia cambogia Extract and Pear Pomace Extract Additively Suppresses Adipogenesis and Enhances Lipolysis in 3T3-L1 Cells

Background:

Inhibition of adipogenesis has been a therapeutic target for reducing obesity and obesity-related disorders such as diabetes, hypertension, atherosclerosis, and cancer. For decades, anti-adipogenic potential of many herbal extracts has been investigated. One example is Garcinia cambogia extract (GE) containing (-)-hydroxycitric acid as an active ingredient. GE is currently marketed as a weight loss supplement, used alone or with other ingredients. Pear pomace extract (PE), another natural product, has been also shown to have anti-adipogenic activity in a recent report.

Objective:

It was tested if the mixture of PE and GE (MIX) would produce more effective anti-adipogenic activity than PE or GE alone.

Materials and Methods:

Differentiation of 3T3-L1 preadipocyte was induced by adding insulin, dexamethasone, and isobutylmethylxanthine and lipid accumulation was measured by Oil Red O staining. Cellular markers for adipogenesis and lipolysis such as CCAAT/enhancer binding protein (C/EBP-α), peroxisome proliferator-activated receptor gamma (PPAR-γ), fatty acid synthase (FAS), and hormone-sensitive lipase (HSL) was measured using immunocytochemistry.

Results:

MIX, compared to PE or GE alone, showed greater inhibition of lipid accumulation. Furthermore, MIX reduced the expression of adipogenesis-related factors C/EBP-α, PPAR-γ, and FAS more than PE or GE alone did. In contrast, the expression of HSL the enzyme required for lipolysis was further enhanced in MIX-treated adipocytes compared to the PE or GE alone treated groups.

Conclusions:

Anti-adipogenic effect of PE and GE appears synergistic, and the MIX may be a useful therapeutic combination for the treatment of obesity and obesity-related diseases.

SUMMARY

PE and GE efficiently inhibited adipocyte differentiation by suppressing the expression of adipogenic transcription factor CEBP-α and PPAR-γ.

PE and GE significantly decreased the expression of adipogenic enzyme FAS.

PE and GE increased the expression of lipid degrading enzyme HSL.

Mixture of PE and GE exhibited additive or moderately synergistic effect on adipocyte differentiation and lipid accumulation.

Abbreviations used: CEBP-a: CCAT/enhancer binding protein alpha, CI: Combination Index, FAS: Fatty acid synthase, GE: Garcinia cambogia extract, HSL: Hormone sensitive lipase, PE: Pear pomace extract, PPAR-γ: Peroxisome proliferator-activated receptor gamma.

Citrus aurantium L. dry extracts promote C/ebpβ expression and improve adipocyte differentiation in 3T3-L1 cells

Metabolic and/or endocrine dysfunction of the white adipose tissue (WAT) contribute to the development of metabolic disorders, such as Type 2 Diabetes (T2D). Therefore, the identification of products able to improve adipose tissue function represents a valuable strategy for the prevention and/or treatment of T2D. In the current study, we investigated the potential effects of dry extracts obtained from Citrus aurantium L. fruit juice (CAde) on the regulation of 3T3-L1 cells adipocyte differentiation and function in vitro. We found that CAde enhances terminal adipocyte differentiation of 3T3-L1 cells raising the expression of CCAAT/enhancer binding protein beta (C/Ebpβ), peroxisome proliferator activated receptor gamma (Pparγ), glucose transporter type 4 (Glut4) and fatty acid binding protein 4 (Fabp4). CAde improves insulin-induced glucose uptake of 3T3-L1 adipocytes, as well. A focused analysis of the phases occurring in the pre-adipocytes differentiation to mature adipocytes furthermore revealed that CAde promotes the early differentiation stage by up-regulating C/ebpβ expression at 2, 4 and 8 h post the adipogenic induction and anticipating the 3T3-L1 cell cycle entry and progression during mitotic clonal expansion (MCE). These findings provide evidence that the exposure to CAde enhances in vitro fat cell differentiation of pre-adipocytes and functional capacity of mature adipocytes, and pave the way to the development of products derived from Citrus aurantium L. fruit juice, which may improve WAT functional capacity and may be effective for the prevention and/or treatment of T2D.

PARP-1 Controls the Adipogenic Transcriptional Program by PARylating C/EBPβ and Modulating Its Transcriptional Activity

Poly(ADP-ribosyl)ation (PARylation) is a post-translational modification of proteins mediated by PARP family members, such as PARP-1. Although PARylation has been studied extensively, few examples of definitive biological roles for site-specific PARylation have been reported. Here we show that C/EBPβ, a key pro-adipogenic transcription factor, is PARylated by PARP-1 on three amino acids in a conserved regulatory domain. PARylation at these sites inhibits C/EBPβ's DNA binding and transcriptional activities and attenuates adipogenesis in various genetic and cell-based models. Interestingly, PARP-1 catalytic activity drops precipitously during the first 48 hr of differentiation, corresponding to a release of C/EBPβ from PARylation-mediated inhibition. This promotes the binding of C/EBPβ at enhancers controlling the expression of adipogenic target genes and continued differentiation. Depletion or chemical inhibition of PARP-1, or mutation of the PARylation sites on C/EBPβ, enhances these early adipogenic events. Collectively, our results provide a clear example of how site-specific PARylation drives biological outcomes.

Enzyme-treated Ecklonia cava extract inhibits adipogenesis through the downregulation of C/EBPα in 3T3-L1 adipocytes

In this study, we examined the inhibitory effects of enzyme- treated Ecklonia cava (EEc) extract on the adipogenesis of 3T3-L1 adipocytes. The components of Ecklonia cava (E. cava) were first separated and purified using the digestive enzymes pectinase (Rapidase® X‑Press L) and cellulase (Rohament® CL). We found that the EEc extract contained three distinct phlorotannins: eckol, dieckol and phlorofucofuroeckol-A. Among the phlorotannins, dieckol was the most abundant in the EEc extract at 16 mg/g. Then we examined the inhibitory effects of EEc extract treatment on differentiation‑related transcription factors and on adipogenesis‑related gene expression in vitro using 3T3-L1 adipocytes. 3T3‑L1 pre‑adipocytes were used to determine the concentrations of the EEc extract and Garcinia cambogia (Gar) extract that did not result in cytotoxicity. Glucose utilization and triglyceride (TG) accumulation in the EEc‑treated adipocytes were similarly inhibited by 50 µg/ml EEc and 200 µg/ml Gar, and these results were confirmed by Oil Red O staining. Protein expression of adipogenesis differentiation‑related transcription factors following treatment with the EEc extract was also examined. Only the expression of CCAAT/enhancer‑binding protein (C/EBP)α was decreased, while there was no effect on the expression of C/EBPβ, C/EBPδ, and peroxisome proliferator‑activated receptor γ (PPARγ). Treatment with the EEc extract decreased the expression levels of adipogenesis‑related genes, in particular sterol regulatory element binding protein‑1c (SREBP‑1c), adipocyte fatty acid binding protein (A‑FABP), fatty acid synthase (FAS) and adiponectin. These results suggest that EEc extract treatment has an inhibitory effect on adipogenesis, specifically by affecting the activation of the C/EBPα signaling pathway and the resulting adipogenesis-related gene expression.

Potential Application of p-Coumaric Acid on Differentiation of C2C12 Skeletal Muscle and 3T3-L1 Preadipocytes-An in Vitro and in Silico Approach

Coumaric acid (CA) is a phenolic acid of the hydroxycinnamic acid family, and it has many biological functions such as anti-oxidant, anti-inflammatory, antidiabetic, anti-ulcer, anti-platelet, anti-cancer activities, etc. In the present study, we planned to analyse the potential molecular function of CA on skeletal muscle and preadipocytes differentiation using PCR and Western blot techniques. First, we analysed the impact of CA on C2C12 skeletal muscle differentiation. It revealed that CA treatment inhibited horse serum-induced skeletal muscle differentiation as evidenced by the decreased expression of early myogenic differentiation markers such as Myogenin and myoD via the AMP activated protein kinase- alpha AMPK-α mediated pathway. Furthermore, the level of lipid accumulation and changes in genes and protein expressions that are associated with lipogenesis and lipolysis were analyzed in 3T3-L1 cells. The Oil Red O staining evidenced that CA treatment inhibited lipid accumulation at the concentration of 0.1 and 0.2 mM. Furthermore, coumaric acid treatment decreased the expression of main transcriptional factors such as CCAAT/enhancer binding protein-alpha (C/EBP-α) and peroxisome proliferator-activated receptor gamma-2 (PPAR-γ2). Subsequently, CA treatment decreased the expression of sterol regulatory element binding protein-1 (SREBP-1), fatty acid synthase (FAS), acetyl CoA carboxylase (ACC) and adiponectin. Finally, we identified conformational changes induced by CA in PPAR-γ2 using computational biology tools. It revealed that CA might downregulate the PPAR-γ2 expression by directly binding with amino acids of PPAR-γ2 by hydrogen at 3.26 distance and hydrophobic interactions at 3.90 contact distances. These data indicated that CA suppressed skeletal muscle and preadipocytes differentiation through downregulation of the main transcriptional factors and their downstream targets.

Dexras1 links glucocorticoids to insulin-like growth factor-1 signaling in adipogenesis

Glucocorticoids are associated with obesity, but the underlying mechanism by which they function remains poorly understood. Previously, we showed that small G protein Dexras1 is expressed by glucocorticoids and leads to adipocyte differentiation. In this study, we explored the mechanism by which Dexras1 mediates adipogenesis and show a link to the insulin-like growth factor-1 (IGF-1) signaling pathway. Without Dexras1, the activation of MAPK and subsequent phosphorylation of CCAAT/enhancer binding protein β (C/EBPβ) is abolished, thereby inhibiting mitotic clonal expansion and further adipocyte differentiation. Dexras1 translocates to the plasma membrane upon insulin or IGF-1 treatment, for which the unique C-terminal domain (amino acids 223–276) is essential. Dexras1-dependent MAPK activation is selectively involved in the IGF-1 signaling, because another Ras protein, H-ras localized to the plasma membrane independently of insulin treatment. Moreover, neither epidermal growth factor nor other cell types shows Dexras1-dependent MAPK activation, indicating the importance of Dexras1 in IGF-1 signaling in adipogenesis. Dexras1 interacts with Shc and Raf, indicating that Dexras1-induced activation of MAPK is largely dependent on the Shc-Grb2-Raf complex. These results suggest that Dexras1 is a critical mediator of the IGF-1 signal to activate MAPK, linking glucocorticoid signaling to IGF-1 signaling in adipogenesis.

Cascade regulation of PPARγ(2) and C/EBPα signaling pathways by celastrol impairs adipocyte differentiation and stimulates lipolysis in 3T3-L1 adipocytes

OBJECTIVE

Celastrol, a triterpene from the root bark of the Chinese medicinal plant Tripterygium wilfordii, has been shown to exhibit anti-oxidant, anti-inflammatory, anti-cancer and insecticidal activities. Also, it has been demonstrated that celastrol has obesity-controlling effects in diet-induced obesity mice. However, direct evidence that celastrol contributes to the development of adipocyte differentiation and lipolysis has not been fully elucidated. Moreover, no previous studies have evaluated whether celastrol may regulate adipogenic transcriptional markers in adipocytes.

MATERIALS/METHODS

In order to address the questions above, we extended previous observations and investigated in vitro celastrol signaling study whether celastrol may regulate differentiation, lipolysis and key adipogenic transcriptional pathways in 3T3-L1 adipocytes.

RESULTS

Treatment of celastrol not only inhibited adipocyte differentiation (lipid accumulation, glyceraldehyde-3-phosphate dehydrogenase activity and triglyceride content) but also increased lipolysis (glycerol release and free fatty acid release) in 3T3-L1 adipocytes. In addition, all celastrol-regulated functional activities were controlled by PPARγ(2) and C/EBPα signaling pathways in duration of celastrol's treatment in 3T3-L1 adipocytes.

CONCLUSION

Our initial data from in vitro celastrol signaling studies suggest novel insights into the role of PPARγ(2) and C/EBPα as probable mediators of the action of celastrol in regulating adipocyte differentiation and lipolysis in 3T3-L1 adipocytes.

In Vivo Deletion of the Cebpa +37 kb Enhancer Markedly Reduces Cebpa mRNA in Myeloid Progenitors but Not in Non-Hematopoietic Tissues to Impair Granulopoiesis

The murine Cebpa gene contains a +37 kb, evolutionarily conserved 440 bp enhancer that directs high-level expression to myeloid progenitors in transgenic mice. The enhancer is bound and activated by Runx1, Scl, GATA2, C/EBPα, c-Myb, Pu.1, and additional Ets factors in myeloid cells. CRISPR/Cas9-mediated replacement of the wild-type enhancer with a variant mutant in its seven Ets sites leads to 20-fold reduction of Cebpa mRNA in the 32Dcl3 myeloid cell line. To determine the effect of deleting the enhancer in vivo, we now characterize C57BL/6 mice in which loxP sites flank a 688 bp DNA segment containing the enhancer. CMV-Cre mediated germline deletion resulted in diminution of the expected number of viable Enh(f/f);CMV-Cre offspring, with 28-fold reduction in marrow Cebpa mRNA but normal levels in liver, lung, adipose, intestine, muscle, and kidney. Cre-transduction of lineage-negative marrow cells in vitro reduced Cebpa mRNA 12-fold, with impairment of granulocytic maturation, morphologic blast accumulation, and IL-3 dependent myeloid colony replating for >12 generations. Exposure of Enh(f/f);Mx1-Cre mice to pIpC led to 14-fold reduction of Cebpa mRNA in GMP or CMP, 30-fold reduction in LSK, and <2-fold reduction in the LSK/SLAM subset. FACS analysis of marrow from these mice revealed 10-fold reduced neutrophils, 3-fold decreased GMP, and 3-fold increased LSK cells. Progenitor cell cycle progression was mildly impaired. Granulocyte and B lymphoid colony forming units were reduced while monocytic and erythroid colonies were increased, with reduced Pu.1 and Gfi1 and increased Egr1 and Klf4 in GMP. Finally, competitive transplantation indicated preservation of functional long-term hematopoietic stem cells upon enhancer deletion and confirmed marrow-intrinsic impairment of granulopoiesis and B cell generation with LSK and monocyte lineage expansion. These findings demonstrate a critical role for the +37 kb Cebpa enhancer for hematopoietic-specific Cebpa expression, with enhancer deletion leading to impaired myelopoiesis and potentially preleukemic progenitor expansion.

Cocoa tea (Camellia ptilophylla) water extract inhibits adipocyte differentiation in mouse 3T3-L1 preadipocytes

Cocoa tea (Camellia ptilophylla) is a naturally decaffeinated tea plant. Previously we found that cocoa tea demonstrated a beneficial effect against high-fat diet induced obesity, hepatic steatosis, and hyperlipidemia in mice. The present study aimed to investigate the anti-adipogenic effect of cocoa tea in vitro using preadipocytes 3T3-L1. Adipogenic differentiation was confirmed by Oil Red O stain, qPCR and Western blot. Our results demonstrated that cocoa tea significantly inhibited triglyceride accumulation in mature adipocytes in a dose-dependent manner. Cocoa tea was shown to suppress the expressions of key adipogenic transcription factors, including peroxisome proliferator-activated receptor gamma (PPAR γ) and CCAAT/enhancer binding protein (C/EBP α). The tea extract was subsequently found to reduce the expressions of adipocyte-specific genes such as sterol regulatory element binding transcription factor 1c (SREBP-1c), fatty acid synthase (FAS), Acetyl-CoA carboxylase (ACC), fatty acid translocase (FAT) and stearoylcoenzyme A desaturase-1 (SCD-1). In addition, JNK, ERK and p38 phosphorylation were inhibited during cocoa tea inhibition of 3T3-L1 adipogenic differentiation. Taken together, this is the first study that demonstrates cocoa tea has the capacity to suppress adipogenesis in pre-adipocyte 3T3-L1 similar to traditional green tea.

Molecular Regulation of Adipogenesis and Potential Anti-Adipogenic Bioactive Molecules

Adipogenesis is the process by which precursor stem cells differentiate into lipid laden adipocytes. Adipogenesis is regulated by a complex and highly orchestrated gene expression program. In mammalian cells, the peroxisome proliferator-activated receptor γ (PPARγ), and the CCAAT/enhancer binding proteins (C/EBPs) such as C/EBPα, β and δ are considered the key early regulators of adipogenesis, while fatty acid binding protein 4 (FABP4), adiponectin, and fatty acid synthase (FAS) are responsible for the formation of mature adipocytes. Excess accumulation of lipids in the adipose tissue leads to obesity, which is associated with cardiovascular diseases, type II diabetes and other pathologies. Thus, investigating adipose tissue development and the underlying molecular mechanisms is vital to develop therapeutic agents capable of curbing the increasing incidence of obesity and related pathologies. In this review, we address the process of adipogenic differentiation, key transcription factors and proteins involved, adipogenic regulators and potential anti-adipogenic bioactive molecules.

Cyclohexane-1,2-dicarboxylic acid diisononyl ester and metabolite effects on rat epididymal stromal vascular fraction differentiation of adipose tissue

Plastics are generally mixed with additives like plasticizers to enhance their flexibility, pliability, and elasticity proprieties. Plasticizers are easily released into the environment and are absorbed mainly through ingestion, dermal contact, and inhalation. One of the main classes of plasticizers, phthalates, has been associated with endocrine and reproductive diseases. In 2002, 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) was introduced in the market for use in plastic materials and articles intended to come into contact with food, and it received final approval from the European Food Safety Authority in 2006. At present, there is limited knowledge about the safety and potential metabolic and endocrine-disrupting properties of DINCH and its metabolites. The purpose of this study was to evaluate the biological effects of DINCH and its active metabolites, cyclohexane-1,2-dicarboxylic acid (CHDA) and cyclohexane-1,2-dicarboxylic acid mono isononyl ester (MINCH), on rat primary stromal vascular fraction (SVF) of adipose tissue. DINCH and its metabolite, CHDA, were not able to directly affect SVF differentiation. However, exposure of SVF to 50 μM and 100 μM concentrations of MINCH affected the expression of Cebpa and Fabp4, thus inducing SVF preadipocytes to accumulate lipids and fully differentiate into mature adipocytes. The effect of MINCH was blocked by the specific peroxisome proliferator-activated receptor (PPAR)-α antagonist, GW6471. Taken together, these results suggest that MINCH is a potent PPAR-α agonist and a metabolic disruptor, capable of inducing SVF preadipocyte differentiation, that may interfere with the endocrine system in mammals.

The +37 kb Cebpa Enhancer Is Critical for Cebpa Myeloid Gene Expression and Contains Functional Sites that Bind SCL, GATA2, C/EBPα, PU.1, and Additional Ets Factors

The murine Cebpa gene contains an evolutionarily conserved 453 bp enhancer located at +37 kb that, together with its promoter, directs expression to myeloid progenitors and to long-term hematopoietic stem cells in transgenic mice. In human acute myeloid leukemia cases, the enhancer lacks point mutations but binds the RUNX1-ETO oncoprotein. The enhancer contains the H3K4me1 and H3K27Ac histone modifications, denoting an active enhancer, at progressively increasing levels as long-term hematopoietic stem cells transition to granulocyte-monocyte progenitors. We previously identified four enhancer sites that bind RUNX1 and demonstrated that their integrity is required for maximal enhancer activity in 32Dcl3 myeloid cells. The +37 kb Cebpa enhancer also contains C/EBP, Ets factor, Myb, GATA, and E-box consensus sites conserved in the human +42 kb CEBPA enhancer. Mutation of the two C/EBP, seven Ets, one Myb, two GATA, or two E-box sites reduces activity of an enhancer-promoter reporter in 32Dcl3 cells. In 293T gel shift assays, exogenous C/EBPα binds both C/EBP sites, c-Myb binds the Myb site, PU.1 binds the second Ets site, PU.1, Fli-1, ERG, and Ets1 bind the sixth Ets site, GATA2 binds both GATA sites, and SCL binds the second E-box. Endogenous hematopoietic RUNX1, PU.1, Fli-1, ERG, C/EBPα, GATA2, and SCL were previously shown to bind the enhancer, and we find that endogenous PU.1 binds the second Ets site in 32Dcl3 cells. Using CRISPR/Cas9, we developed 32Dcl3 lines in which the wild-type enhancer alleles are replaced with a variant mutant in the seven Ets sites. These lines have 20-fold reduced Cebpa mRNA when cultured in IL-3 or G-CSF, demonstrating a critical requirement for enhancer integrity for optimal Cebpa expression. In addition, these results indicate that the +37 kb Cebpa enhancer is the focus of multiple regulatory transcriptional pathways that impact its expression during normal hematopoiesis and potentially during myeloid transformation.

The regulation of oxytocin receptor gene expression during adipogenesis

Although it has been reported that oxytocin stimulates lipolysis in adipocytes, changes in the expression of oxytocin receptor (OTR) mRNA in adipogenesis are still unknown. The present study aimed to investigate the expression of OTR mRNA during adipocyte differentiation and fat accumulation in adipocytes. OTR mRNA was highly expressed in adipocytes prepared from mouse adipose tissues compared to stromal-vascular cells. OTR mRNA expression was increased during the adipocyte differentiation of 3T3-L1 cells. OTR expression levels were higher in subcutaneous and epididymal adipose tissues of 14-week-old male mice compared to 7-week-old male mice. Levels of OTR mRNA expression were higher in adipose tissues at four different sites of mice fed a high-fat diet than in those of mice fed a normal diet. The OTR expression level was also increased by refeeding for 4 h after fasting for 16 h. Oxytocin significantly induced lipolysis in 3T3-L1 adipocytes. In conclusion, a new regulatory mechanism is demonstrated for oxytocin to control the differentiation and fat accumulation in adipocytes via activation of OTR as a part of the hypothalamic-pituitary-adipose axis.

C/EBPα in normal and malignant myelopoiesis

CCAAT/enhancer binding protein α (C/EBPα) dimerizes via its leucine zipper (LZ) domain to bind DNA via its basic region and activate transcription via N-terminal trans-activation domains. The activity of C/EBPα is modulated by several serine/threonine kinases and via sumoylation, its gene is activated by RUNX1 and additional transcription factors, its mRNA stability is modified by miRNAs, and its mRNA is subject to translation control that affects AUG selection. In addition to inducing differentiation, C/EBPα inhibits cell cycle progression and apoptosis. Within hematopoiesis, C/EBPα levels increase as long-term stem cells progress to granulocyte-monocyte progenitors (GMP). Absence of C/EBPα prevents GMP formation, and higher levels are required for granulopoiesis compared to monopoiesis. C/EBPα interacts with AP-1 proteins to bind hybrid DNA elements during monopoiesis, and induction of Gfi-1, C/EBPε, KLF5, and miR-223 by C/EBPα enables granulopoiesis. The CEBPA ORF is mutated in approximately 10 % of acute myeloid leukemias (AML), leading to expression of N-terminally truncated C/EBPαp30 and C-terminal, in-frame C/EBPαLZ variants, which inhibit C/EBPα activities but also play additional roles during myeloid transformation. RUNX1 mutation, CEBPA promoter methylation, Trib1 or Trib2-mediated C/EBPαp42 degradation, and signaling pathways leading to C/EBPα serine 21 phosphorylation reduce C/EBPα expression or activity in additional AML cases.

Sinensetin enhances adipogenesis and lipolysis by increasing cyclic adenosine monophosphate levels in 3T3-L1 adipocytes

Sinensetin is a rare polymethoxylated flavone (PMF) found in certain citrus fruits. In this study, we investigated the effects of sinensetin on lipid metabolism in 3T3-L1 cells. Sinensetin promoted adipogenesis in 3T3-L1 preadipocytes growing in incomplete differentiation medium, which did not contain 3-isobutyl-1-methylxanthine. Sinensetin up-regulated expression of the adipogenic transcription factors peroxisome proliferator-activated receptor γ, CCAAT/enhancer-binding protein (C/EBP) α, and sterol regulatory element-binding protein 1c. It also potentiated expression of C/EBPβ and activation of cAMP-responsive element-binding protein. Sinensetin enhanced activation of protein kinase A and increased intracellular cAMP levels in 3T3-L1 preadipocytes. In mature 3T3-L1 adipocytes, sinensetin stimulated lipolysis via a cAMP pathway. Taken together, these results suggest that sinensetin enhances adipogenesis and lipolysis by increasing cAMP levels in adipocytes.

Adipose tissues and thyroid hormones

The maintenance of energy balance is regulated by complex homeostatic mechanisms, including those emanating from adipose tissue. The main function of the adipose tissue is to store the excess of metabolic energy in the form of fat. The energy stored as fat can be mobilized during periods of energy deprivation (hunger, fasting, diseases). The adipose tissue has also a homeostatic role regulating energy balance and functioning as endocrine organ that secretes substances that control body homeostasis. Two adipose tissues have been identified: white and brown adipose tissues (WAT and BAT) with different phenotype, function and regulation. WAT stores energy, while BAT dissipates energy as heat. Brown and white adipocytes have different ontogenetic origin and lineage and specific markers of WAT and BAT have been identified. “Brite” or beige adipose tissue has been identified in WAT with some properties of BAT. Thyroid hormones exert pleiotropic actions, regulating the differentiation process in many tissues including the adipose tissue. Adipogenesis gives raise to mature adipocytes and is regulated by several transcription factors (c/EBPs, PPARs) that coordinately activate specific genes, resulting in the adipocyte phenotype. T3 regulates several genes involved in lipid mobilization and storage and in thermogenesis. Both WAT and BAT are targets of thyroid hormones, which regulate genes crucial for their proper function: lipogenesis, lipolysis, thermogenesis, mitochondrial function, transcription factors, the availability of nutrients. T3 acts directly through specific TREs in the gene promoters, regulating transcription factors. The deiodinases D3, D2, and D1 regulate the availability of T3. D3 is activated during proliferation, while D2 is linked to the adipocyte differentiation program, providing T3 needed for lipogenesis and thermogenesis. We examine the differences between BAT, WAT and brite/beige adipocytes and the process that lead to activation of UCP1 in WAT and the presence of BAT in humans and its relevance.

RARγ-C-Fos-PPARγ2 signaling rather than ROS generation is critical for all-trans retinoic acid-inhibited adipocyte differentiation

Obesity has become a worldwide public health problem, which is mainly determined by excess energy intake and adipose tissue expansion. Adipose tissue expansion can occur through hyperplasia (adipocyte differentiation) or hypertrophy. Retinoic acid was shown to inhibit adipocyte differentiation. However, the molecular mechanism is unclear. In the study, we found that all-trans-retinoic acid (ATRA) inhibited 3T3-L1 adipocyte differentiation. We did not observe significant apoptosis in differentiated adipocytes treated by ATRA. ATRA increased ROS generation and disturbed redox balance. However, antioxidant treatment did not ameliorate the reduction of lipid accumulation induced by ATRA, indicating that ROS generation was not involved in ATRA-inhibited adipocyte differentiation. ATRA reduced C/EBPα, PPARγ and its target gene expression. In the presence of ATRA, retinoic acid receptor (RAR) α/γ expression was increased. Inhibition of RARγ, but not RARα, blocked ATRA-induced reduction of PPARγ2 expression. ATRA induced a profound interaction between RARγ and C-Fos protein, reflected by Co-IP results. C-Fos was found to exhibit a differentiation-dependent DNA binding activity to PPARγ2 promoter. RARγ inhibitor significantly suppressed ATRA-inhibited DNA binding activity of C-Fos to PPARγ2 promoter, indicating that downregulation of C-Fos activity mediated activation of RARγ-exerted reduction of PPARγ2 expression and thus inhibition of adipocyte differentiation induced by ATRA. Taken together, these data demonstrates that RARγ-C-Fos-PPARγ2 signaling rather than ROS generation is critical for ATRA-inhibited adipocyte differentiation.

Identification of KMU-3, a novel derivative of gallic acid, as an inhibitor of adipogenesis

Differentiation of preadipocyte, also called adipogenesis, leads to the phenotype of mature adipocyte. Excessive adipogenesis, however, is largely linked to the development of obesity. Herein we investigated a library of 53 novel chemicals, generated from a number of polyphenolic natural compounds, on adipogenesis. Strikingly, among the chemicals tested, KMU-3, a derivative of gallic acid, strongly suppressed lipid accumulation during the differentiation of 3T3-L1 preadipocytes into adipocytes. On mechanistic levels, KMU-3 inhibited expressions of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), and fatty acid synthase (FAS) during adipocyte differentiation. Moreover, KMU-3 reduced expressions of adipokines, including retinol binding protein-4 (RBP-4), leptin, and regulated on activation, normal T cell expressed and secreted (RANTES) during adipocyte differentiation. Of further note, KMU-3 rapidly blocked the phosphorylation of signal transducer and activator of transcription-3 (STAT-3) during the early stage of adipogenesis. Importantly, pharmacological inhibition studies revealed that AG490, a JAK-2/STAT-3 inhibitor suppressed adipogenesis and STAT-3 phosphorylation, implying that early blockage of STAT-3 activity is crucial for the KMU-3-mediated anti-adipogenesis. These findings demonstrate firstly that KMU-3 inhibits adipogenesis by down-regulating STAT-3, PPAR-γ, C/EBP-α, and FAS. This work shows that KMU-3 is an inhibitor of adipogenesis and thus may have therapeutic potential against obesity.

LKB1 signalling attenuates early events of adipogenesis and responds to adipogenic cues

cAMP-response element-binding protein (CREB) is required for the induction of adipogenic transcription factors such as CCAAT/enhancer-binding proteins (C/EBPs). Interestingly, it is known from studies in other tissues that LKB1 and its substrates AMP-activated protein kinase (AMPK) and salt-inducible kinases (SIKs) negatively regulate gene expression by phosphorylating the CREB co-activator CRTC2 and class IIa histone deacetylases (HDACs), which results in their exclusion from the nucleus where they co-activate or inhibit their targets. In this study, we show that AMPK/SIK signalling is acutely attenuated during adipogenic differentiation of 3T3-L1 preadipocytes, which coincides with the dephosphorylation and nuclear translocation of CRTC2 and HDAC4. When subjected to differentiation, 3T3-L1 preadipocytes in which the expression of LKB1 was stably reduced using shRNA (Lkb1-shRNA), as well as Lkb1-knockout mouse embryonic fibroblasts (Lkb1(-/-) MEFs), differentiated more readily into adipocyte-like cells and accumulated more triglycerides compared with scrambled-shRNA-expressing 3T3-L1 cells or Wt MEFs. In addition, the phosphorylation of CRTC2 and HDAC4 was reduced, and the mRNA expression of adipogenic transcription factors Cebpa, peroxisome proliferator-activated receptor γ (Pparg) and adipocyte-specific proteins such as hormone-sensitive lipase (HSL), fatty acid synthase (FAS), aP2, GLUT4 and adiponectin was increased in the absence of LKB1. The mRNA and protein expression of Ddit3/CHOP10, a dominant-negative member of the C/EBP family, was reduced in Lkb1-shRNA-expressing cells, providing a potential mechanism for the up-regulation of Pparg and Cebpa expression. These results support the hypothesis that LKB1 signalling keeps preadipocytes in their non-differentiated form.

The Cebpa +37-kb enhancer directs transgene expression to myeloid progenitors and to long-term hematopoietic stem cells

C/EBPα is expressed preferentially in myeloid compared with lymphoid or erythroid cells and directs myeloid lineage specification. C/EBPα is also expressed at lower levels in HSCs and in several nonhematopoietic tissues. The Cebpa gene has a conserved, 450-bp segment at +37 kb that harbors enhancer-specific epigenetic marks and is activate in a myeloid cell line. Herein, we characterize transgenic C57BL/6 mice, in which the Cebpa enhancer and 845-bp promoter regulate a hCD4 reporter. FACS analysis, in vitro colony assays, and in vivo competitive and secondary transplantation revealed that myeloid but not MEPs or lymphoid progenitors and also functional LT-HSCs are found almost exclusively in the Cebpa-hCD4(+) compared with hCD4(-) marrow population. hCD4(+) CMP yielded predominantly myeloid, whereas hCD4(-) CMP generated mainly Meg/E colonies. Providing insight into control of CMP maturation, Cebpa and Pu.1 RNAs were preferentially expressed in hCD4(+) CMP, Scl, Gata2, Gata1, Klf1, Ets1, and Fli1 predominated in hCD4(-) CMP, and Runx1, Myb, HoxA9, and Erg levels were similar in both. Cebpa-hCD4 transgene expression was lacking in multiple nonhematopoietic tissues. In summary, the +37-kb Cebpa enhancer and promoter are sufficient for marrow myeloid progenitor and LT-HSC-specific expression.

Functional O-GlcNAc modifications: implications in molecular regulation and pathophysiology

O-linked β-N-acetylglucosamine (O-GlcNAc) is a regulatory post-translational modification of intracellular proteins. The dynamic and inducible cycling of the modification is governed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) in response to UDP-GlcNAc levels in the hexosamine biosynthetic pathway (HBP). Due to its reliance on glucose flux and substrate availability, a major focus in the field has been on how O-GlcNAc contributes to metabolic disease. For years this post-translational modification has been known to modify thousands of proteins implicated in various disorders, but direct functional connections have until recently remained elusive. New research is beginning to reveal the specific mechanisms through which O-GlcNAc influences cell dynamics and disease pathology including clear examples of O-GlcNAc modification at a specific site on a given protein altering its biological functions. The following review intends to focus primarily on studies in the last half decade linking O-GlcNAc modification of proteins with chromatin-directed gene regulation, developmental processes, and several metabolically related disorders including Alzheimer's, heart disease and cancer. These studies illustrate the emerging importance of this post-translational modification in biological processes and multiple pathophysiologies.

Apigenin isolated from Daphne genkwa Siebold et Zucc. inhibits 3T3-L1 preadipocyte differentiation through a modulation of mitotic clonal expansion

AIMS

Obesity develops when energy intake chronically exceeds total energy expenditure. We sought to assess whether the flavonoid-rich fraction of crude extracts from Daphne genkwa Siebold et Zuccarini (GFF) might inhibit adipogenesis of 3T3-L1 cells.

MAIN METHODS

Cell viability of 3T3-L1 preadipocytes was assessed by MTT assays, and lipid accumulation was measured by Oil Red O. Adipogenesis related factors were checked by Western blot analysis. Flow cytometry was used to analyze the mitotic cell cycle during the mitotic clonal expansion phase.

KEY FINDINGS

Among five flavonoids isolated from GFF, only apigenin potently inhibited the differentiation of 3T3-L1 cells. Apigenin reduced CCAAT/enhancer binding protein (C/EBP) α and peroxisome proliferator-activated receptor γ levels. Apigenin-treated 3T3-L1 cells failed to undergo clonal expansion during the early phase of adipocyte differentiation. Apigenin arrested cell cycle progression at the G0/G1 phase. This effect was associated with a marked decrease in cyclin D1 and cyclin-dependent kinase 4 expression, with the concomitant and sustained expression of p27(Kip1). In addition, apigenin inhibited the DNA-binding activity of C/EBPβ in differentiating 3T3-L1 cells by down-regulating the 35kDa isoform of C/EBPβ (liver-enriched activating protein) and up-regulating the expression of two different sets of C/EBP inhibitors: C/EBP homologous protein and the phospho-liver-enriched inhibitory protein isoform of C/EBPβ.

SIGNIFICANCE

These findings suggest that apigenin can prevent 3T3-L1 preadipocyte differentiation by the inhibition of the mitotic clonal expansion and the adipogenesis related factors and upregulation of the expression of multiple C/EBPβ inhibitors.

Proteome profiling of mitotic clonal expansion during 3T3-L1 adipocyte differentiation using iTRAQ-2DLC-MS/MS

Mitotic clonal expansion (MCE) is one of the important events taking place at the early stage during 3T3-L1 adipocyte differentiation. To investigate the mechanism underlying this process, we carried out a temporal proteomic analysis to profile the dynamic changes in MCE. Using 8-plex-iTRAQ-2DLC-MS/MS analysis, 3152 proteins were quantified during the initial 28 h of 3T3-L1 adipogenesis. Functional analysis was performed on 595 proteins with maximum or minimum quantities at 20 h of adipogenic induction that were potentially involved in MCE, which identified PI3K/AKT/mTOR as the most relevant pathway. Among the 595 proteins, PKM2 (Pyruvate kinase M2), a patterned protein identified as a potential target gene of C/EBPβ in our previous work, was selected for further investigation. Network analysis suggested positive correlations among C/EBPβ, PIN1, and PKM2, which may be related with the PI3K-AKT pathway. Knockdown of PKM2 with siRNA inhibited both MCE and adipocyte differentiation of 3T3-L1 cells. Moreover, PKM2 was down-regulated at both the mRNA level and the protein level upon the knockdown of C/EBPβ. And overexpressed PKM2 can partially restore MCE, although it did not restore terminal adipocyte differentiation, which was inhibited by siC/EBPβ. Thus, PKM2, potentially regulated by C/EBPβ, is involved in MCE during adipocyte differentiation. The dynamic proteome changes quantified here provide a promising basis for revealing molecular mechanism regulating adipogenesis.